Sound Attenuation - Main Duct to Branches

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When main ducts are split into branches the sound power level - L_w - is reduced according the size of the branch, or amount of air to the branch.

The attenuation can be calculated as

dL_w = 10 log(A_b/A_m)         (1)

where

dL_w = attenuation (dB)

A_b = branch area (m², ft²)

A_m = main duct area (m², ft²)

The attenuation is indicated in the diagram below:

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